Field of the Invention
This invention relates to marine seismology and more particularly relates to the design of ocean bottom seismic autonomous underwater vehicles (AUVs) and the deployment, retrieval, and operation thereof.
Description of the Related Art
Marine seismic data acquisition and processing generates a profile (image) of a geophysical structure under the seafloor. Reflection seismology is a method of geophysical exploration to determine the properties of the Earth's subsurface, which is especially helpful in determining an accurate location of oil and gas reservoirs or any targeted features. Marine reflection seismology is based on using a controlled source of energy (typically acoustic energy) that sends the energy through a body of water and subsurface geologic formations. The transmitted acoustic energy propagates downwardly through the subsurface as acoustic waves, also referred to as seismic waves or signals. By measuring the time it takes for the reflections or refractions to come back to seismic receivers (also known as seismic data recorders or nodes), it is possible to evaluate the depth of features causing such reflections. These features may be associated with subterranean hydrocarbon deposits or other geological structures of interest.
There are many methods to record the reflections from a seismic wave off the geological structures present in the surface beneath the seafloor. In one method, a marine vessel tows an array of seismic data recorders provided in streamers. In another method, seismic data recorders are placed directly on the ocean bottom by a variety of mechanisms, including by the use of one or more of Autonomous Underwater Vehicles (AUVs), Remotely Operated Vehicles (ROVs), by dropping or diving from a surface or subsurface vessel, or by attaching autonomous nodes to a cable that is deployed behind a marine vessel. The data recorders may be discrete, autonomous units, with no direct connection to other nodes or to the marine vessel, where data is stored and recorded.
Emerging technologies in marine seismic surveys need a fast and cost-effective system for deploying and recovering seismic receivers that are configured to operate underwater, and in particular ocean bottom seismic nodes. Newer technologies use AUVs that have a propulsion system and are programmed to move to desired positions and record seismic data. In general, the basic structure and operation of a seismic AUV is well known to those of ordinary skill. For example, Applicant's U.S. Pat. No. 9,090,319, incorporated herein by reference, discloses one type of autonomous underwater vehicle for marine seismic surveys. As another example, Applicant's U.S. Patent Publication No. 2017/0137098, incorporated herein by reference, discloses another type of AUV for seabed seismic applications.
Because a seismic survey may require hundreds if not thousands of AUVs for a particular survey, an AUV is needed that is easy to operate and relatively straightforward and cost-effective to manufacture. However, existing technologies for deploying a seismic AUV to the ocean bottom (and the related AUV designs) are not cost effective and present many operational problems. A need exists for an improved AUV that is more cost effective and less complex, one that is lighter and requires less power, and one that is easier to maintain and repair. An improved AUV is needed that more effectively couples to the seabed and can travel to and from a particular point on the seabed without using as much power as may be required by known seismic AUVs.